Preheat your oven to 350°F (175°C) and line your muffin tin with cupcake liners.
In a mixing bowl, whisk together the all-purpose flour, baking powder, and salt. Set aside.
In a separate bowl, combine the melted butter and granulated sugar. Mix until smooth. Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.
Pour in the buttermilk and mix until just combined.
Gradually add the dry ingredient mixture into the wet ingredients, stirring gently until no flour streaks remain. Be careful not to overmix.
Gently fold in the rainbow sprinkles, ensuring they are evenly distributed throughout the batter.
Divide the batter evenly among the cupcake liners, filling each about 2/3 full.
Bake in the preheated oven for 18-20 minutes, or until a toothpick inserted into the center comes out clean.
Remove the cupcakes from the oven and let them cool in the tin for 5 minutes. Then transfer them to a cooling rack to cool completely.
Once cooled, frost your cupcakes with your choice of frosting and finish with additional sprinkles.
